This has been a 2,5 year long active thread on the Norwegian Audi forum. Alot of the guys over here are running E85 on their 1,8t and 2,7t engines. Not seen it in any 2,0 TFSI engines yet.

None with any corrosive issues or leaking hoses/fuellines.
Ethanol is not corrosive like Methanol.

The dowsides that have been discovered here is that the Ethanol will clean out your fuellines because of the alkohol levels cleans it and prob you will have to change your fuelfilter in a while.
Your engine will be a little more diffiult to start when its really cold outside.
The consumption will increase some.

Benefits is that it is actually cheaper. (over here atleas) dont know what the costs are un US.
The engine will burn alot colder. The only documentet example ive seen on this is a friends S2. He got one program for 93 oct and one for E85. 502 dyno HP on the 93 oct. 586 dyno HP on the E85. And the combustion was 150 degrees celcius colder than with 93 oct.

The problems most have run into is that the amount of fuel needs to be increased alot to make it work proberly. Change of injectors, fuelpumps and so on. You need alot more of E85 compared to normal octane to get the right mix. Prob not good for our cars since the issues with the fuelsystem already.

Ofcourse you will get the best HP benefits with the right tune and all, but all that have talked about this here have good experience with it on the engines i specified above.

Would i recommend for your car: No. Not without any decent logging, AFR measuring, monitored in a dyno or something for the first times.